Jurors quickly agreed, deliberating for four hours before convicting Yang of first-degree murder in Reuter’s Oct. 4, 2007 slaying. The nine-man, three-woman jury also convicted the 43-year-old Yang of a second charge: the intentional homicide of an unborn child.

Yang stood between her attorneys as the verdicts were being read but showed no emotion. Gayle also showed no emotion. A couple of Reuter’s relatives wiped tears from their eyes.

Reuter, 42, was nearly seven months pregnant with Gayle’s daughter — a baby she already had named Skylar Reyne — when she was shot to death in her Deerfield condominium.

Yang was a real estate agent who also had carried on a sporadic sexual relationship with Gayle and — according to prosecutors — killed Reuter because she had become “obsessed” with the former Bears’ star.

“The defendant was obsessed with eliminating the competition,” prosecutor Ari Fisz told jurors before they began deliberating.

More than a dozen of Reuter’s relatives were in the jammed courtroom when the verdicts were delivered, sitting separately from Gayle, his mother and his attorney.

Yang, who didn’t testify during her trial, faces a mandatory life sentence when she is sentenced later this year by Judge Christopher Stride.

Fisz urged jurors to convict Yang, saying there is “an overwhelming amount of evidence” tying her to the murder, including two secretly recorded conversations in which Yang calmly describes the killing in detail.

“She is absolutely, clearly, completely guilty,” Fisz said, pointing across the courtroom at the petite Yang, who sat between her attorneys, wearing glasses with her long graying hair neatly tied in a braid.

He played two snippets of the 2009 recordings between Yang and a friend, Christi Paschen, including one in which Yang says she repeatedly shot Reuter until she collapsed to the floor. Yang then describes firing one additional bullet into the dying woman.

“I took one last shot in the head — finished her off,” Yang can be heard saying on the tape.

But defense attorney William Hedrick said prosecutors had no physical evidence or eyewitnesses linking Yang to the slaying.

“This case is best characterized as a theory searching for evidence,’’ Hedrick said, contending police focused on Yang as the only suspect within four days of the killing.

“Marni Yang became suspect number one to the exclusion of every one else in the world,” Hedrick said.

Hedrick also denied that Yang was obsessed with Gayle, instead contending the divorced mother of three had a long-term boyfriend and was busy living her own life.

“She had a full life,” Hedrick said of Yang, though he acknowledged she knew Gayle.

“That she liked Shaun Gayle and was a victim of Shaun Gayle, there can be no dispute,” said Hedrick during his closing argument, though he declined outside the courtroom to expand on those comments.

He and co-counsel Jeffrey Learner argued during the trial that Gayle had been involved with as many as 18 or 19 women at the time of Reuter’s death — a claim denied by Gayle’s attorney.

He ripped Paschen — a self-described psychic who had claimed to be in a secret military unit because of her mental abilities — as lacking “an ounce of credibility.

“She lied from the moment she hit the witness stand, and she never stopped,’’ Hedrick said.

He painted the recorded conversations between Paschen and Yang as two friends trying to “one up” each other in telling wild tales.

“We know truly that Marni Yang is making this up,’’ Hedrick said, noting that Yang never mentioned key details of the killings to Paschen, including that she allegedly used a homemade silencer on her 9 mm pistol, or that the gun repeatedly jammed.

But prosecutors said Yang’s description was corroborated by other witnesses, including a pathologist who testified that Reuter died of a fatal gunshot wound to the head.

And it was Yang, not Paschen, describing the murder on the secret recordings, Fisz reminded jurors. “You might think she’s goofy,” Fisz said of Paschen. “Whatever you think of her, she can press record.”

Fisz described the murder as “an execution.”

“It was a very well-planned, carefully thought-out execution,” he said. “For months, the defendant planned how she was going to carry out this murder.”

Fisz put on rubber gloves and took out six bullets that had struck Reuter and been recovered from the crime scene.

Then, one by one, he slowly dropped them onto a metal cart, where they echoed loudly in the courtroom.

“We have six bullets that hit Rhoni,” he said.

Two of the bullets also struck her unborn child causing wounds that a pathologist testified would have killed the baby even if Reuter had survived.

Fisz finished his closing arguments by recounting how Yang said that as Reuter was dying, she had only the strength left to kick Yang.

“You have the power to do more,” Fisz told jurors. “With your verdicts, tell Rhoni you know who did this. With your verdicts, tell Rhoni you’re going to give her justice.”